Some modern communication systems, such as InfiniBand systems, require high-speed electrical signals to be converted into high-speed optical signals. Because optical functionality is relatively expensive when compared to electronic functionality, the overall system costs can generally be minimized by using optical components, such as lasers and fiber optic cables, that are as low performance as can be tolerated. In order to minimize optical jitter, such communication systems utilize signal conditioning circuits in the electrical domain to reduce jitter from the electrical signals that are converted into optical signals. FIG. 1 presents a prior art optical transmitter 100.
The optical transmitter 100 includes a phase-locked-loop 105. The phase-locked-loop 105 receives a reference clock signal 110 and generates a plurality of clock signals. Each of the plurality of clock signals has a frequency that is approximately equal to the frequency of the input data signal 115. However, the phase of each of the clock signals differ. For example, each clock signal may have a phase that differs by a predetermined multiple, such as π/6 radians, from its phase-adjacent clock signal. In this way, an entire cycle (2π radians) of the clock signal can be covered by evenly spaced (in terms of phase) clock signals.
The optical transmitter 100 also includes a clock-recovery circuit 120. The clock-recovery circuit 120 is coupled to the phase-locked-loop 105. In addition, the clock-recovery circuit 120 is operable to receive an input data signal 115. As is known in the art, the clock-recovery circuit 120 is operable to extract timing information from the input data signal 115.
The optical transmitter 100 also includes a latch-decision circuit 125. The latch-decision circuit 125 is coupled to the clock-recovery circuit 120. The latch-decision circuit 125 may also be operable to receive the input data signal 115. The latch-decision circuit 125 is operable to determine, using algorithms known in the art, an appropriate time to latch the input data signal 115 so that the input data signal 115 is sampled near the center portion of each pulse that corresponds to either logic “1” or logic “0.” Such a determination is based upon the timing information that is received from the clock-recovery circuit 120 and information extracted from the input data signal 115.
The optical transmitter 100 also includes a latch 130. The strobe input of the latch 130 is coupled to the latch-decision circuit 125. The data input of the latch 130 is operable to receive the input data signal 115.
The optical transmitter 100 also includes an electro-optical converter 135. The electro-optical converter 135 is coupled to the latch 130. The electro-optical converter 135, which typically includes a laser, is operable to generate an optical signal that is compliant with the InfiniBand specification.
The phase-locked-loop 105, the clock recovery circuit 120, the latch decision circuit 125, and the latch 130 work together to minimize the jitter in the input data signal 115. Thus, a low performance electro-optical converter 135 can be utilized to reduce the cost of the optical transmitter 100.
In order to increase the bandwidth of InfiniBand links, the InfiniBand specification provides for optical transmitters that include multiple electro-optical converters. For example, one InfiniBand link, which is known as a 4 X link, includes 4 electro-optical converters. Another InfiniBand link, which is known as a 12 X link, includes 12 electro-optical converters.
FIG. 2 presents a portion of a prior art optical transmitter 200 that includes multiple electro-optical converters. The optical transmitter 200 includes a first phase-locked-loop 205 and a first clock-recovery circuit 220. The first clock-recovery circuit 220 is coupled to the first phase-locked-loop 205 and is operable to receive a first input data signal 215. The optical transmitter 200 also includes a first latch-decision circuit 225 that is coupled to the first clock-recovery circuit 220 and may also be operable to receive the first input data signal 215. The optical transmitter 200 also includes a first latch 230 that is coupled to the first latch-decision circuit 225 and is operable to receive the first input data signal 215. The optical transmitter 200 also includes a first electro-optical converter 235 that is coupled to the first latch 230.
As shown in FIG. 2, the optical transmitter 200 also includes a second phase-locked-loop 240, a second clock-recovery circuit 250, a second latch-decision circuit 255, a second latch 260, and a second electro-optical converter 265.
The first phase-locked-loop 205, the first clock recovery circuit 220, the first latch-decision circuit 225, and the first latch 230 work together to minimize the jitter in the first input data signal 215. Similarly, the second phase-locked-loop 240, the second clock-recovery circuit 250, the second latch-decision circuit 255, and the second latch 260 work together to minimize the jitter in the second input data signal 245. Thus, low performance electro-optical converters 235 and 265 can be utilized to reduce the cost of the optical transmitter 200.
While the optical transmitter 200 can generate high quality optical signals that are compliant with the InfiniBand specification, the cost of such a transmitter is significant. Thus, a need exists for a cost-reduced optical transmitter that utilizes a reduced die-size and uses lower power than the prior art, and that is operable to receive high-speed optical input signals.